Dr Piper told newspapers that "if we discover the genes involved with ageing, we should be able to delay ageing itself."

In animals caloric restriction, or eating less, has been found to minimise the outward effects of ageing, such as greying hair and fur, and improve energy levels in old age, provided the animals are supplied with sufficient vitamins, minerals and protein.

The effect in humans is relatively untested, as humans who practice caloric restriction usually have low BMIs, between 18 and 21, which can creep into eating disorder territory.

The traditional Okinawa diet eaten by the indigenous people of the Ryukyu Islands, which boasts one of teh highest longevity rates in the world, is a good example of how a low-calorie diet can extend life.

The islanders' traditional diet was on average 20 per cent lower in calories that of mainland Japanese, and sweet potato was the staple, rather than rice.

Intermittent caloric restriction, where high-fat and low-fat diets are alternated, is another approach to diet that may have life-extending effects.

In a small study carried out in Ohio, mice fed according to intermittent caloric restriction outlived another group of mice who were given a high-fat diet. diet.